In some circumstances, the operator of radio telephone equipment must perform the necessary communication while he is simultaneously engaged in other activities.
For example, a driver of a vehicle must communicate by his radio equipment while he is steering the vehicle, a worker at a construction or a quarrying site must use his radio telephone equipment while he is doing his job at the site, and a fireman must use his radio telephone equipment while he is engaged in a fire extinguishing operation.
In all these circumstances, the radio operator cannot use his hands or his eyes for the operation of his radio telephone equipment. In the specification of a United States Pat. application No. 688,911/76 filed on May 21, 1976, now U.S. Pat. No. 4,087,636, by the same applicant of the present invention under the title of TRANSMIT-RECEIVE CIRCUIT CHANGING SWITCH SYSTEM, (hereinafter called the prior application) a transmit-receive circuit changing switch system is disclosed in which the circuit changing switch is operated by an electric signal generated from a low-frequency signal produced by the operator's particular voice. Owing to this switch system, the press-to-talk manual switch is eliminated, and the operator's hands are released from the job of operating the manual press-to-talk switch.
Even then, the operator's eyes are engaged in confirming the state of the circuit connection when the state of the circuit connection is indicated by such a visual indicator as a pilot lamp. This will be a substantial handicap for the operator under some circumstances.